1. Field of the Invention
This invention relates to a method of preparing pure 1,3,5-trinitro-1,3,5-triazacyclohexane by the direct liquid phase nitration of hexamethylenetetramine.
2. Description of the Prior Art
1,3,5-trinitro-1,3,5-triazacyclohexane is currently prepared by a two-step procedure known in the art as the Bachman process. In this process, a mixture of ammonium nitrate and hexamine nitrate is added to a solution of nitric acid in acetic anhydride. While the product yield is about 70%, the intermediates and the final product contain about 10% of the contaminant 1,3,5,7-tetraaza-1,3,5,7-tetranitrocyclooctane. Further purification steps are required to reduce the presence of the contaminant to acceptable levels. These purification steps diminish the final yield of 1,3,5-trinitro-1,3,5-triazacyclohexane.
It is also known to prepare 1,3,5-trinitro-1,3,5-triazacyclohexane by direct liquid nitration using dinitrogen pentoxide dissolved in a non-aqueous neutral solvent such as a hydrocarbon or halogenated hydrocarbon. Although the process has been described as producing relatively pure 1,3,5-trinitro-1,3,5-triazacyclohexane, the use of a hydrocarbon or halogenated hydrocarbon solvent results in impurities which must be removed by additional processing. Additionally, scale-up problems are caused by the limited half-life of didinitrogen pentoxide in hydrocarbon or halogenated hydrocarbon solvents.
The nitration of hexamethylenetetramine to produce 1,3,5-trinitro-1,3,5-triazacyclohexane has also been achieved using concentrated nitric acid and small amounts of ammonium salts such as NH4NO3 and (NH4)2SO4 to prevent runaway reaction and reduce the decomposition of the 1,3,5-trinitro-1,3,5-triazacyclohexane to undesirable by-products.